The present invention generally relates to a coating machine and more particularly, to a device for automatically controlling coating amount for use in the coating machine.
As shown in FIGS. 1 and 2, conventionally, in coating machines, it has been so arranged as disclosed, for example, in Japanese Laid-Open Utility Model Application No. 131869/1982 (Jikkaisho 57-131869) that an applicator roll 1 for applying paint to a sheet-like workpiece 22 pressed onto a backup roll 23 is secured to a first table 4. A pickup roll 2 for picking up paint stored in a pickup pan is secured to a second table 5, while a metering roll 3 is secured to a third table 6. The first table 4, the second table 5 and the third table 6 are slidably mounted on a base 19. Furthermore a first pressure adjusting mechanism 41 adjusts the contact pressure between the backup roll 23 and the applicator roll 1 by moving the first table 4 relative to the base 19. Mechanism 41 is mounted on the base 19 and engages the first table 4. A second pressure adjusting mechanism 42 adjusts the contact pressure between the applicator roll 1 and the pickup roll 2 by moving the second table 5 relative to the first table 4. Mechanism 42 is mounted on the first table 4 and engage the second table 5. A third pressure adjusting mechanism 43 adjust a contact pressure between the pickup roll 2 and the metering roll 3 by moving the third table 6 relative to the second table 5. Mechanism 43 is mounted on the second table 5 and engages the third table 6. Thus, thickness of a coating film on the workpiece 22 can be adjusted by operating the first, second and third pressure adjusting mechanisms 41, 42 and 43.
It should be understood that the applicator roll 1 is required to be quickly retracted away from the backup roll 23 just before a seam 26 of the workpiece 22 passes therebetween. To this end, a cylinder 20 is attached to the base 19 and is coupled with the first pressure adjusting mechanism 41 through a lever 33. Just before the seam 26 of the workpiece 22 passes between the backup roll 23 and the applicator roll 1, the first table 4 is quickly moved relative to the base 19 by the cylinder 20 in the leftward direction in FIG. 1, whereby the applicator roll 1 is quickly retracted away from the backup roll 23.
As best shown in FIG. 2, each of the first and second pressure adjusting mechanisms 41, 42 and 43 comprises a worm gearing composed of a worm 28 and a worm wheel 29, a rotary device (not shown) such as a hydraulic motor, a DC motor, etc. for driving the worm 28, a screw shaft 30 and a nut 14 (FIG. 1). The screw shaft 30 is unrotatably but axially movably mounted in the worm wheel 29 by a key 31 fitted into a key way 32 of the screw shaft 30 and is attached, at one end thereof, to the level 33. The first, second pressure adjusting mechanisms and the 41, 42 and 43 are operated by means of a manual handle based on skill of an operator. Thus, the prior art pressure and adjusting mechanisms have the disadvantages that skill of the operator is required for the operation and it is impossible to maintain each of the pressures between adjacent ones of the backup roll, the applicator roll, the pickup roll and the metering roll and the pickup roll at predetermined pressure values. Furthermore, the known pressure and adjusting mechanisms have such inconveniences that it is extremely difficult to operate them at higher speed and make them larger in size. Meanwhile, the known pressure adjusting mechanisms have been disadvantageous in that it is impossible to cope with minute changes in each pressure and the clearance due to rotation, swell, etc. of each roll. Moreover, the prior art pressure adjusting mechanisms have such a disadvantage that, in case each of the first, second and third tables are driven by a hydraulic motor or a DC motor through the worm gearing having a considerable play, it is impossible to accurately control each of contact pressures between adjacent ones of the rolls in forward and reverse rotations of the worm gearing. In addition, the known pressure adjusting mechanisms have such an inconvenience that, when a restrictive torque is continuously generated in the DC motor, its commutator is heated, thereby resulting in seizing thereof.